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class="sidebar-link">面试官：为什么data属性是一个函数而不是一个对象？</a></li><li><a href="/fe/vue/data_object_add_attrs.html" class="sidebar-link">面试官：动态给vue的data添加一个新的属性时会发生什么？怎样解决？</a></li><li><a href="/fe/vue/components_plugin.html" class="sidebar-link">面试官：Vue中组件和插件有什么区别？</a></li><li><a href="/fe/vue/communication.html" class="sidebar-link">面试官：Vue组件之间的通信方式都有哪些？</a></li><li><a href="/fe/vue/nexttick.html" class="sidebar-link">面试官：Vue中的$nextTick有什么作用？</a></li><li><a href="/fe/vue/mixin.html" aria-current="page" class="active sidebar-link">Mixin 混入</a><ul class="sidebar-sub-headers"><li class="sidebar-sub-header"><a href="/fe/vue/mixin.html#一、是什么" class="sidebar-link">一、是什么</a></li><li class="sidebar-sub-header"><a href="/fe/vue/mixin.html#二、优缺点" class="sidebar-link">二、优缺点</a></li><li class="sidebar-sub-header"><a href="/fe/vue/mixin.html#三、使用场景" class="sidebar-link">三、使用场景</a></li><li class="sidebar-sub-header"><a href="/fe/vue/mixin.html#三、源码分析" class="sidebar-link">三、源码分析</a></li><li class="sidebar-sub-header"><a href="/fe/vue/mixin.html#参考文献" class="sidebar-link">参考文献</a></li></ul></li><li><a href="/fe/vue/slot.html" class="sidebar-link">面试官：说说你对slot的理解？slot使用场景有哪些？</a></li><li><a href="/fe/vue/observable.html" class="sidebar-link">面试官：Vue.observable你有了解过吗？说说看</a></li><li><a href="/fe/vue/key.html" class="sidebar-link">Key的理解</a></li><li><a href="/fe/vue/keepalive.html" class="sidebar-link">面试官：说说你对keep-alive的理解是什么？</a></li><li><a href="/fe/vue/modifier.html" class="sidebar-link">面试官：Vue常用的修饰符有哪些有什么应用场景</a></li><li><a href="/fe/vue/directive.html" class="sidebar-link">面试官：你有写过自定义指令吗？自定义指令的应用场景有哪些？</a></li><li><a href="/fe/vue/filter.html" class="sidebar-link">面试官：Vue中的过滤器了解吗？过滤器的应用场景有哪些？</a></li><li><a href="/fe/vue/vnode.html" class="sidebar-link">虚拟DOM</a></li><li><a href="/fe/vue/diff.html" class="sidebar-link">Diff 算法</a></li><li><a href="/fe/vue/axios.html" class="sidebar-link">面试官：Vue项目中有封装过axios吗？主要是封装哪方面的？</a></li><li><a href="/fe/vue/axios_code.html" class="sidebar-link">面试官：你了解axios的原理吗？有看过它的源码吗？</a></li><li><a href="/fe/vue/ssr.html" class="sidebar-link">面试官：SSR解决了什么问题？有做过SSR吗？你是怎么做的？</a></li><li><a href="/fe/vue/structure.html" class="sidebar-link">面试官：说下你的vue项目的目录结构，如果是大型项目你该怎么划分结构和划分组件呢？</a></li><li><a href="/fe/vue/permission.html" class="sidebar-link">面试官：vue要做权限管理该怎么做？如果控制到按钮级别的权限怎么做？</a></li><li><a href="/fe/vue/cors.html" class="sidebar-link">面试官：Vue项目中你是如何解决跨域的呢？</a></li><li><a href="/fe/vue/404.html" class="sidebar-link">面试官：vue项目本地开发完成后部署到服务器后报404是什么原因呢？</a></li><li><a href="/fe/vue/error.html" class="sidebar-link">面试官：你是怎么处理vue项目中的错误的？</a></li><li><a href="/fe/vue/vue_router.html" class="sidebar-link">Vue Router</a></li><li><a href="/fe/vue/vue-debounce-throttle.html" class="sidebar-link">vue防抖调研</a></li></ul></section></li><li><section class="sidebar-group collapsable depth-0"><p class="sidebar-heading"><span>Vue3</span> <span class="arrow right"></span></p> <!----></section></li><li><section class="sidebar-group collapsable depth-0"><p class="sidebar-heading"><span>React</span> <span class="arrow right"></span></p> <!----></section></li><li><section class="sidebar-group collapsable depth-0"><p class="sidebar-heading"><span>Webpack</span> <span class="arrow right"></span></p> <!----></section></li><li><section class="sidebar-group collapsable depth-0"><p class="sidebar-heading"><span>Node.js</span> <span class="arrow right"></span></p> <!----></section></li><li><section class="sidebar-group collapsable depth-0"><p class="sidebar-heading"><span>性能优化</span> <span class="arrow right"></span></p> <!----></section></li><li><section class="sidebar-group collapsable depth-0"><p class="sidebar-heading"><span>手写代码</span> <span class="arrow right"></span></p> <!----></section></li></ul> </aside> <main class="page"> <div class="theme-default-content content__default"><h1 id="mixin-混入"><a href="#mixin-混入" class="header-anchor">#</a> Mixin 混入</h1> <h2 id="一、是什么"><a href="#一、是什么" class="header-anchor">#</a> 一、是什么</h2> <p><code>Mixin</code>是面向对象程序设计语言中的类，提供了方法的实现。其他类可以访问<code>mixin</code>类的方法而不必成为其子类</p> <p><code>Mixin</code>类通常作为功能模块使用，在需要该功能时“混入”，有利于代码复用又避免了多继承的复杂</p> <h3 id="vue中的mixin"><a href="#vue中的mixin" class="header-anchor">#</a> Vue中的mixin</h3> <p>先来看一下官方定义</p> <blockquote><p><code>mixin</code>（混入），提供了一种非常灵活的方式，来分发 <code>Vue</code> 组件中的可复用功能。</p></blockquote> <p>本质其实就是一个<code>js</code>对象，它可以包含我们组件中任意功能选项，如<code>data</code>、<code>components</code>、<code>methods</code>、<code>created</code>、<code>computed</code>等等</p> <p>我们只要将共用的功能以对象的方式传入 <code>mixins</code>选项中，当组件使用 <code>mixins</code>对象时所有<code>mixins</code>对象的选项都将被混入该组件本身的选项中来</p> <p>在<code>Vue</code>中我们可以<strong>局部混入</strong>跟<strong>全局混入</strong></p> <h3 id="局部混入"><a href="#局部混入" class="header-anchor">#</a> 局部混入</h3> <p>定义一个<code>mixin</code>对象，有组件<code>options</code>的<code>data</code>、<code>methods</code>属性</p> <div class="language-js extra-class"><pre class="language-js"><code><span class="token keyword">var</span> myMixin <span class="token operator">=</span> <span class="token punctuation">{</span>
  <span class="token function-variable function">created</span><span class="token operator">:</span> <span class="token keyword">function</span> <span class="token punctuation">(</span><span class="token punctuation">)</span> <span class="token punctuation">{</span>
    <span class="token keyword">this</span><span class="token punctuation">.</span><span class="token function">hello</span><span class="token punctuation">(</span><span class="token punctuation">)</span>
  <span class="token punctuation">}</span><span class="token punctuation">,</span>
  methods<span class="token operator">:</span> <span class="token punctuation">{</span>
    <span class="token function-variable function">hello</span><span class="token operator">:</span> <span class="token keyword">function</span> <span class="token punctuation">(</span><span class="token punctuation">)</span> <span class="token punctuation">{</span>
      console<span class="token punctuation">.</span><span class="token function">log</span><span class="token punctuation">(</span><span class="token string">'hello from mixin!'</span><span class="token punctuation">)</span>
    <span class="token punctuation">}</span>
  <span class="token punctuation">}</span>
<span class="token punctuation">}</span>
</code></pre></div><p>组件通过<code>mixins</code>属性调用<code>mixin</code>对象</p> <div class="language-js extra-class"><pre class="language-js"><code>Vue<span class="token punctuation">.</span><span class="token function">component</span><span class="token punctuation">(</span><span class="token string">'componentA'</span><span class="token punctuation">,</span><span class="token punctuation">{</span>
  mixins<span class="token operator">:</span> <span class="token punctuation">[</span>myMixin<span class="token punctuation">]</span>
<span class="token punctuation">}</span><span class="token punctuation">)</span>
</code></pre></div><p>该组件在使用的时候，混合了<code>mixin</code>里面的方法，在自动执行<code>create</code>生命钩子，执行<code>hello</code>方法</p> <h3 id="全局混入"><a href="#全局混入" class="header-anchor">#</a> 全局混入</h3> <p>通过<code>Vue.mixin()</code>进行全局的混入</p> <div class="language-js extra-class"><pre class="language-js"><code>Vue<span class="token punctuation">.</span><span class="token function">mixin</span><span class="token punctuation">(</span><span class="token punctuation">{</span>
  <span class="token function-variable function">created</span><span class="token operator">:</span> <span class="token keyword">function</span> <span class="token punctuation">(</span><span class="token punctuation">)</span> <span class="token punctuation">{</span>
      console<span class="token punctuation">.</span><span class="token function">log</span><span class="token punctuation">(</span><span class="token string">&quot;全局混入&quot;</span><span class="token punctuation">)</span>
    <span class="token punctuation">}</span>
<span class="token punctuation">}</span><span class="token punctuation">)</span>
</code></pre></div><p>使用全局混入需要特别注意，因为它会影响到每一个组件实例（包括第三方组件）</p> <p>PS：全局混入常用于插件的编写</p> <h3 id="注意事项"><a href="#注意事项" class="header-anchor">#</a> 注意事项</h3> <p>当组件存在与<code>mixin</code>对象相同的选项的时候，进行递归合并的时候组件的选项会覆盖<code>mixin</code>的选项</p> <p>但是如果相同选项为生命周期钩子的时候，会合并成一个数组，先执行<code>mixin</code>的钩子，再执行组件的钩子</p> <h2 id="二、优缺点"><a href="#二、优缺点" class="header-anchor">#</a> 二、优缺点</h2> <p>弊端：</p> <ol><li>难以追溯的方法与属性。</li> <li>覆盖、同名。</li> <li>同一组件引用两次同一mixin文件时，复杂且可读性差。</li></ol> <h2 id="三、使用场景"><a href="#三、使用场景" class="header-anchor">#</a> 三、使用场景</h2> <p>在日常的开发中，我们经常会遇到在不同的组件中经常会需要用到一些相同或者相似的代码，这些代码的功能相对独立</p> <p>这时，可以通过<code>Vue</code>的<code>mixin</code>功能将相同或者相似的代码提出来</p> <p>举个例子</p> <p>定义一个<code>modal</code>弹窗组件，内部通过<code>isShowing</code>来控制显示</p> <div class="language-js extra-class"><pre class="language-js"><code><span class="token keyword">const</span> Modal <span class="token operator">=</span> <span class="token punctuation">{</span>
  template<span class="token operator">:</span> <span class="token string">'#modal'</span><span class="token punctuation">,</span>
  <span class="token function">data</span><span class="token punctuation">(</span><span class="token punctuation">)</span> <span class="token punctuation">{</span>
    <span class="token keyword">return</span> <span class="token punctuation">{</span>
      isShowing<span class="token operator">:</span> <span class="token boolean">false</span>
    <span class="token punctuation">}</span>
  <span class="token punctuation">}</span><span class="token punctuation">,</span>
  methods<span class="token operator">:</span> <span class="token punctuation">{</span>
    <span class="token function">toggleShow</span><span class="token punctuation">(</span><span class="token punctuation">)</span> <span class="token punctuation">{</span>
      <span class="token keyword">this</span><span class="token punctuation">.</span>isShowing <span class="token operator">=</span> <span class="token operator">!</span><span class="token keyword">this</span><span class="token punctuation">.</span>isShowing<span class="token punctuation">;</span>
    <span class="token punctuation">}</span>
  <span class="token punctuation">}</span>
<span class="token punctuation">}</span>
</code></pre></div><p>定义一个<code>tooltip</code>提示框，内部通过<code>isShowing</code>来控制显示</p> <div class="language-js extra-class"><pre class="language-js"><code><span class="token keyword">const</span> Tooltip <span class="token operator">=</span> <span class="token punctuation">{</span>
  template<span class="token operator">:</span> <span class="token string">'#tooltip'</span><span class="token punctuation">,</span>
  <span class="token function">data</span><span class="token punctuation">(</span><span class="token punctuation">)</span> <span class="token punctuation">{</span>
    <span class="token keyword">return</span> <span class="token punctuation">{</span>
      isShowing<span class="token operator">:</span> <span class="token boolean">false</span>
    <span class="token punctuation">}</span>
  <span class="token punctuation">}</span><span class="token punctuation">,</span>
  methods<span class="token operator">:</span> <span class="token punctuation">{</span>
    <span class="token function">toggleShow</span><span class="token punctuation">(</span><span class="token punctuation">)</span> <span class="token punctuation">{</span>
      <span class="token keyword">this</span><span class="token punctuation">.</span>isShowing <span class="token operator">=</span> <span class="token operator">!</span><span class="token keyword">this</span><span class="token punctuation">.</span>isShowing<span class="token punctuation">;</span>
    <span class="token punctuation">}</span>
  <span class="token punctuation">}</span>
<span class="token punctuation">}</span>
</code></pre></div><p>通过观察上面两个组件，发现两者的逻辑是相同，代码控制显示也是相同的，这时候<code>mixin</code>就派上用场了</p> <p>首先抽出共同代码，编写一个<code>mixin</code></p> <div class="language-js extra-class"><pre class="language-js"><code><span class="token keyword">const</span> toggle <span class="token operator">=</span> <span class="token punctuation">{</span>
  <span class="token function">data</span><span class="token punctuation">(</span><span class="token punctuation">)</span> <span class="token punctuation">{</span>
    <span class="token keyword">return</span> <span class="token punctuation">{</span>
      isShowing<span class="token operator">:</span> <span class="token boolean">false</span>
    <span class="token punctuation">}</span>
  <span class="token punctuation">}</span><span class="token punctuation">,</span>
  methods<span class="token operator">:</span> <span class="token punctuation">{</span>
    <span class="token function">toggleShow</span><span class="token punctuation">(</span><span class="token punctuation">)</span> <span class="token punctuation">{</span>
      <span class="token keyword">this</span><span class="token punctuation">.</span>isShowing <span class="token operator">=</span> <span class="token operator">!</span><span class="token keyword">this</span><span class="token punctuation">.</span>isShowing<span class="token punctuation">;</span>
    <span class="token punctuation">}</span>
  <span class="token punctuation">}</span>
<span class="token punctuation">}</span>
</code></pre></div><p>两个组件在使用上，只需要引入<code>mixin</code></p> <div class="language-js extra-class"><pre class="language-js"><code><span class="token keyword">const</span> Modal <span class="token operator">=</span> <span class="token punctuation">{</span>
  template<span class="token operator">:</span> <span class="token string">'#modal'</span><span class="token punctuation">,</span>
  mixins<span class="token operator">:</span> <span class="token punctuation">[</span>toggle<span class="token punctuation">]</span>
<span class="token punctuation">}</span><span class="token punctuation">;</span>
 
<span class="token keyword">const</span> Tooltip <span class="token operator">=</span> <span class="token punctuation">{</span>
  template<span class="token operator">:</span> <span class="token string">'#tooltip'</span><span class="token punctuation">,</span>
  mixins<span class="token operator">:</span> <span class="token punctuation">[</span>toggle<span class="token punctuation">]</span>
<span class="token punctuation">}</span>
</code></pre></div><p>通过上面小小的例子，让我们知道了<code>Mixin</code>对于封装一些可复用的功能如此有趣、方便、实用</p> <h2 id="三、源码分析"><a href="#三、源码分析" class="header-anchor">#</a> 三、源码分析</h2> <p>首先从<code>Vue.mixin</code>入手</p> <p>源码位置：/src/core/global-api/mixin.js</p> <div class="language-js extra-class"><pre class="language-js"><code><span class="token keyword">export</span> <span class="token keyword">function</span> <span class="token function">initMixin</span> <span class="token punctuation">(</span><span class="token parameter">Vue<span class="token operator">:</span> GlobalAPI</span><span class="token punctuation">)</span> <span class="token punctuation">{</span>
  Vue<span class="token punctuation">.</span><span class="token function-variable function">mixin</span> <span class="token operator">=</span> <span class="token keyword">function</span> <span class="token punctuation">(</span><span class="token parameter">mixin<span class="token operator">:</span> Object</span><span class="token punctuation">)</span> <span class="token punctuation">{</span>
    <span class="token keyword">this</span><span class="token punctuation">.</span>options <span class="token operator">=</span> <span class="token function">mergeOptions</span><span class="token punctuation">(</span><span class="token keyword">this</span><span class="token punctuation">.</span>options<span class="token punctuation">,</span> mixin<span class="token punctuation">)</span>
    <span class="token keyword">return</span> <span class="token keyword">this</span>
  <span class="token punctuation">}</span>
<span class="token punctuation">}</span>
</code></pre></div><p>主要是调用<code>merOptions</code>方法</p> <p>源码位置：/src/core/util/options.js</p> <div class="language-js extra-class"><pre class="language-js"><code><span class="token keyword">export</span> <span class="token keyword">function</span> <span class="token function">mergeOptions</span> <span class="token punctuation">(</span>
  <span class="token parameter">parent<span class="token operator">:</span> Object<span class="token punctuation">,</span>
  child<span class="token operator">:</span> Object<span class="token punctuation">,</span>
  vm<span class="token operator">?</span><span class="token operator">:</span> Component</span>
<span class="token punctuation">)</span><span class="token operator">:</span> Object <span class="token punctuation">{</span>

<span class="token keyword">if</span> <span class="token punctuation">(</span>child<span class="token punctuation">.</span>mixins<span class="token punctuation">)</span> <span class="token punctuation">{</span> <span class="token comment">// 判断有没有mixin 也就是mixin里面挂mixin的情况 有的话递归进行合并</span>
    <span class="token keyword">for</span> <span class="token punctuation">(</span><span class="token keyword">let</span> i <span class="token operator">=</span> <span class="token number">0</span><span class="token punctuation">,</span> l <span class="token operator">=</span> child<span class="token punctuation">.</span>mixins<span class="token punctuation">.</span>length<span class="token punctuation">;</span> i <span class="token operator">&lt;</span> l<span class="token punctuation">;</span> i<span class="token operator">++</span><span class="token punctuation">)</span> <span class="token punctuation">{</span>
    parent <span class="token operator">=</span> <span class="token function">mergeOptions</span><span class="token punctuation">(</span>parent<span class="token punctuation">,</span> child<span class="token punctuation">.</span>mixins<span class="token punctuation">[</span>i<span class="token punctuation">]</span><span class="token punctuation">,</span> vm<span class="token punctuation">)</span>
    <span class="token punctuation">}</span>
<span class="token punctuation">}</span>

  <span class="token keyword">const</span> options <span class="token operator">=</span> <span class="token punctuation">{</span><span class="token punctuation">}</span> 
  <span class="token keyword">let</span> key
  <span class="token keyword">for</span> <span class="token punctuation">(</span>key <span class="token keyword">in</span> parent<span class="token punctuation">)</span> <span class="token punctuation">{</span>
    <span class="token function">mergeField</span><span class="token punctuation">(</span>key<span class="token punctuation">)</span> <span class="token comment">// 先遍历parent的key 调对应的strats[XXX]方法进行合并</span>
  <span class="token punctuation">}</span>
  <span class="token keyword">for</span> <span class="token punctuation">(</span>key <span class="token keyword">in</span> child<span class="token punctuation">)</span> <span class="token punctuation">{</span>
    <span class="token keyword">if</span> <span class="token punctuation">(</span><span class="token operator">!</span><span class="token function">hasOwn</span><span class="token punctuation">(</span>parent<span class="token punctuation">,</span> key<span class="token punctuation">)</span><span class="token punctuation">)</span> <span class="token punctuation">{</span> <span class="token comment">// 如果parent已经处理过某个key 就不处理了</span>
      <span class="token function">mergeField</span><span class="token punctuation">(</span>key<span class="token punctuation">)</span> <span class="token comment">// 处理child中的key 也就parent中没有处理过的key</span>
    <span class="token punctuation">}</span>
  <span class="token punctuation">}</span>
  <span class="token keyword">function</span> <span class="token function">mergeField</span> <span class="token punctuation">(</span><span class="token parameter">key</span><span class="token punctuation">)</span> <span class="token punctuation">{</span>
    <span class="token keyword">const</span> strat <span class="token operator">=</span> strats<span class="token punctuation">[</span>key<span class="token punctuation">]</span> <span class="token operator">||</span> defaultStrat
    options<span class="token punctuation">[</span>key<span class="token punctuation">]</span> <span class="token operator">=</span> <span class="token function">strat</span><span class="token punctuation">(</span>parent<span class="token punctuation">[</span>key<span class="token punctuation">]</span><span class="token punctuation">,</span> child<span class="token punctuation">[</span>key<span class="token punctuation">]</span><span class="token punctuation">,</span> vm<span class="token punctuation">,</span> key<span class="token punctuation">)</span> <span class="token comment">// 根据不同类型的options调用strats中不同的方法进行合并</span>
  <span class="token punctuation">}</span>
  <span class="token keyword">return</span> options
<span class="token punctuation">}</span>
</code></pre></div><p>从上面的源码，我们得到以下几点：</p> <ul><li>优先递归处理 <code>mixins</code></li> <li>先遍历合并<code>parent</code> 中的<code>key</code>，调用<code>mergeField</code>方法进行合并，然后保存在变量<code>options</code></li> <li>再遍历 <code>child</code>，合并补上 <code>parent</code> 中没有的<code>key</code>，调用<code>mergeField</code>方法进行合并，保存在变量<code>options</code></li> <li>通过 <code>mergeField</code> 函数进行了合并</li></ul> <p>下面是关于<code>Vue</code>的几种类型的合并策略</p> <ul><li>替换型</li> <li>合并型</li> <li>队列型</li> <li>叠加型</li></ul> <h3 id="替换型"><a href="#替换型" class="header-anchor">#</a> 替换型</h3> <p>替换型合并有<code>props</code>、<code>methods</code>、<code>inject</code>、<code>computed</code></p> <div class="language-js extra-class"><pre class="language-js"><code>strats<span class="token punctuation">.</span>props <span class="token operator">=</span>
strats<span class="token punctuation">.</span>methods <span class="token operator">=</span>
strats<span class="token punctuation">.</span>inject <span class="token operator">=</span>
strats<span class="token punctuation">.</span><span class="token function-variable function">computed</span> <span class="token operator">=</span> <span class="token keyword">function</span> <span class="token punctuation">(</span>
  <span class="token parameter">parentVal<span class="token operator">:</span> <span class="token operator">?</span>Object<span class="token punctuation">,</span>
  childVal<span class="token operator">:</span> <span class="token operator">?</span>Object<span class="token punctuation">,</span>
  vm<span class="token operator">?</span><span class="token operator">:</span> Component<span class="token punctuation">,</span>
  key<span class="token operator">:</span> string</span>
<span class="token punctuation">)</span><span class="token operator">:</span> <span class="token operator">?</span>Object <span class="token punctuation">{</span>
  <span class="token keyword">if</span> <span class="token punctuation">(</span><span class="token operator">!</span>parentVal<span class="token punctuation">)</span> <span class="token keyword">return</span> childVal <span class="token comment">// 如果parentVal没有值，直接返回childVal</span>
  <span class="token keyword">const</span> ret <span class="token operator">=</span> Object<span class="token punctuation">.</span><span class="token function">create</span><span class="token punctuation">(</span><span class="token keyword">null</span><span class="token punctuation">)</span> <span class="token comment">// 创建一个第三方对象 ret</span>
  <span class="token function">extend</span><span class="token punctuation">(</span>ret<span class="token punctuation">,</span> parentVal<span class="token punctuation">)</span> <span class="token comment">// extend方法实际是把parentVal的属性复制到ret中</span>
  <span class="token keyword">if</span> <span class="token punctuation">(</span>childVal<span class="token punctuation">)</span> <span class="token function">extend</span><span class="token punctuation">(</span>ret<span class="token punctuation">,</span> childVal<span class="token punctuation">)</span> <span class="token comment">// 把childVal的属性复制到ret中</span>
  <span class="token keyword">return</span> ret
<span class="token punctuation">}</span>
strats<span class="token punctuation">.</span>provide <span class="token operator">=</span> mergeDataOrFn
</code></pre></div><p>同名的<code>props</code>、<code>methods</code>、<code>inject</code>、<code>computed</code>会被后来者代替</p> <h3 id="合并型"><a href="#合并型" class="header-anchor">#</a> 合并型</h3> <p>和并型合并有：<code>data</code></p> <div class="language-js extra-class"><pre class="language-js"><code>strats<span class="token punctuation">.</span><span class="token function-variable function">data</span> <span class="token operator">=</span> <span class="token keyword">function</span><span class="token punctuation">(</span><span class="token parameter">parentVal<span class="token punctuation">,</span> childVal<span class="token punctuation">,</span> vm</span><span class="token punctuation">)</span> <span class="token punctuation">{</span>    
    <span class="token keyword">return</span> <span class="token function">mergeDataOrFn</span><span class="token punctuation">(</span>
        parentVal<span class="token punctuation">,</span> childVal<span class="token punctuation">,</span> vm
    <span class="token punctuation">)</span>
<span class="token punctuation">}</span><span class="token punctuation">;</span>

<span class="token keyword">function</span> <span class="token function">mergeDataOrFn</span><span class="token punctuation">(</span><span class="token parameter">parentVal<span class="token punctuation">,</span> childVal<span class="token punctuation">,</span> vm</span><span class="token punctuation">)</span> <span class="token punctuation">{</span>    
    <span class="token keyword">return</span> <span class="token keyword">function</span> <span class="token function">mergedInstanceDataFn</span><span class="token punctuation">(</span><span class="token punctuation">)</span> <span class="token punctuation">{</span>        
        <span class="token keyword">var</span> childData <span class="token operator">=</span> <span class="token function">childVal</span><span class="token punctuation">.</span><span class="token function">call</span><span class="token punctuation">(</span>vm<span class="token punctuation">,</span> vm<span class="token punctuation">)</span> <span class="token comment">// 执行data挂的函数得到对象</span>
        <span class="token keyword">var</span> parentData <span class="token operator">=</span> <span class="token function">parentVal</span><span class="token punctuation">.</span><span class="token function">call</span><span class="token punctuation">(</span>vm<span class="token punctuation">,</span> vm<span class="token punctuation">)</span>        
        <span class="token keyword">if</span> <span class="token punctuation">(</span>childData<span class="token punctuation">)</span> <span class="token punctuation">{</span>            
            <span class="token keyword">return</span> <span class="token function">mergeData</span><span class="token punctuation">(</span>childData<span class="token punctuation">,</span> parentData<span class="token punctuation">)</span> <span class="token comment">// 将2个对象进行合并                                 </span>
        <span class="token punctuation">}</span> <span class="token keyword">else</span> <span class="token punctuation">{</span>            
            <span class="token keyword">return</span> parentData <span class="token comment">// 如果没有childData 直接返回parentData</span>
        <span class="token punctuation">}</span>
    <span class="token punctuation">}</span>
<span class="token punctuation">}</span>

<span class="token keyword">function</span> <span class="token function">mergeData</span><span class="token punctuation">(</span><span class="token parameter">to<span class="token punctuation">,</span> <span class="token keyword">from</span></span><span class="token punctuation">)</span> <span class="token punctuation">{</span>    
    <span class="token keyword">if</span> <span class="token punctuation">(</span><span class="token operator">!</span>from<span class="token punctuation">)</span> <span class="token keyword">return</span> to    
    <span class="token keyword">var</span> key<span class="token punctuation">,</span> toVal<span class="token punctuation">,</span> fromVal<span class="token punctuation">;</span>    
    <span class="token keyword">var</span> keys <span class="token operator">=</span> Object<span class="token punctuation">.</span><span class="token function">keys</span><span class="token punctuation">(</span>from<span class="token punctuation">)</span><span class="token punctuation">;</span>   
    <span class="token keyword">for</span> <span class="token punctuation">(</span><span class="token keyword">var</span> i <span class="token operator">=</span> <span class="token number">0</span><span class="token punctuation">;</span> i <span class="token operator">&lt;</span> keys<span class="token punctuation">.</span>length<span class="token punctuation">;</span> i<span class="token operator">++</span><span class="token punctuation">)</span> <span class="token punctuation">{</span>
        key <span class="token operator">=</span> keys<span class="token punctuation">[</span>i<span class="token punctuation">]</span><span class="token punctuation">;</span>
        toVal <span class="token operator">=</span> to<span class="token punctuation">[</span>key<span class="token punctuation">]</span><span class="token punctuation">;</span>
        fromVal <span class="token operator">=</span> from<span class="token punctuation">[</span>key<span class="token punctuation">]</span><span class="token punctuation">;</span>    
        <span class="token comment">// 如果不存在这个属性，就重新设置</span>
        <span class="token keyword">if</span> <span class="token punctuation">(</span><span class="token operator">!</span>to<span class="token punctuation">.</span><span class="token function">hasOwnProperty</span><span class="token punctuation">(</span>key<span class="token punctuation">)</span><span class="token punctuation">)</span> <span class="token punctuation">{</span>
            <span class="token function">set</span><span class="token punctuation">(</span>to<span class="token punctuation">,</span> key<span class="token punctuation">,</span> fromVal<span class="token punctuation">)</span><span class="token punctuation">;</span>
        <span class="token punctuation">}</span>      
        <span class="token comment">// 存在相同属性，合并对象</span>
        <span class="token keyword">else</span> <span class="token keyword">if</span> <span class="token punctuation">(</span><span class="token keyword">typeof</span> toVal <span class="token operator">==</span><span class="token string">&quot;object&quot;</span> <span class="token operator">&amp;&amp;</span> <span class="token keyword">typeof</span> fromVal <span class="token operator">==</span><span class="token string">&quot;object&quot;</span><span class="token punctuation">)</span> <span class="token punctuation">{</span>
            <span class="token function">mergeData</span><span class="token punctuation">(</span>toVal<span class="token punctuation">,</span> fromVal<span class="token punctuation">)</span><span class="token punctuation">;</span>
        <span class="token punctuation">}</span>
    <span class="token punctuation">}</span>    
    <span class="token keyword">return</span> to
<span class="token punctuation">}</span>
</code></pre></div><p><code>mergeData</code>函数遍历了要合并的 data 的所有属性，然后根据不同情况进行合并：</p> <ul><li>当目标 data 对象不包含当前属性时，调用 <code>set</code> 方法进行合并（set方法其实就是一些合并重新赋值的方法）</li> <li>当目标 data 对象包含当前属性并且当前值为纯对象时，递归合并当前对象值，这样做是为了防止对象存在新增属性</li></ul> <h3 id="队列性"><a href="#队列性" class="header-anchor">#</a> 队列性</h3> <p>队列性合并有：全部生命周期和<code>watch</code></p> <div class="language-js extra-class"><pre class="language-js"><code><span class="token keyword">function</span> <span class="token function">mergeHook</span> <span class="token punctuation">(</span>
  <span class="token parameter">parentVal<span class="token operator">:</span> <span class="token operator">?</span>Array<span class="token operator">&lt;</span>Function<span class="token operator">&gt;</span><span class="token punctuation">,</span>
  childVal<span class="token operator">:</span> <span class="token operator">?</span>Function <span class="token operator">|</span> <span class="token operator">?</span>Array<span class="token operator">&lt;</span>Function<span class="token operator">&gt;</span></span>
<span class="token punctuation">)</span><span class="token operator">:</span> <span class="token operator">?</span>Array<span class="token operator">&lt;</span>Function<span class="token operator">&gt;</span> <span class="token punctuation">{</span>
  <span class="token keyword">return</span> childVal
    <span class="token operator">?</span> parentVal
      <span class="token operator">?</span> parentVal<span class="token punctuation">.</span><span class="token function">concat</span><span class="token punctuation">(</span>childVal<span class="token punctuation">)</span>
      <span class="token operator">:</span> Array<span class="token punctuation">.</span><span class="token function">isArray</span><span class="token punctuation">(</span>childVal<span class="token punctuation">)</span>
        <span class="token operator">?</span> childVal
        <span class="token operator">:</span> <span class="token punctuation">[</span>childVal<span class="token punctuation">]</span>
    <span class="token operator">:</span> parentVal
<span class="token punctuation">}</span>

<span class="token constant">LIFECYCLE_HOOKS</span><span class="token punctuation">.</span><span class="token function">forEach</span><span class="token punctuation">(</span><span class="token parameter">hook</span> <span class="token operator">=&gt;</span> <span class="token punctuation">{</span>
  strats<span class="token punctuation">[</span>hook<span class="token punctuation">]</span> <span class="token operator">=</span> mergeHook
<span class="token punctuation">}</span><span class="token punctuation">)</span>

<span class="token comment">// watch</span>
strats<span class="token punctuation">.</span><span class="token function-variable function">watch</span> <span class="token operator">=</span> <span class="token keyword">function</span> <span class="token punctuation">(</span>
  <span class="token parameter">parentVal<span class="token punctuation">,</span>
  childVal<span class="token punctuation">,</span>
  vm<span class="token punctuation">,</span>
  key</span>
<span class="token punctuation">)</span> <span class="token punctuation">{</span>
  <span class="token comment">// work around Firefox's Object.prototype.watch...</span>
  <span class="token keyword">if</span> <span class="token punctuation">(</span>parentVal <span class="token operator">===</span> nativeWatch<span class="token punctuation">)</span> <span class="token punctuation">{</span> parentVal <span class="token operator">=</span> <span class="token keyword">undefined</span><span class="token punctuation">;</span> <span class="token punctuation">}</span>
  <span class="token keyword">if</span> <span class="token punctuation">(</span>childVal <span class="token operator">===</span> nativeWatch<span class="token punctuation">)</span> <span class="token punctuation">{</span> childVal <span class="token operator">=</span> <span class="token keyword">undefined</span><span class="token punctuation">;</span> <span class="token punctuation">}</span>
  <span class="token comment">/* istanbul ignore if */</span>
  <span class="token keyword">if</span> <span class="token punctuation">(</span><span class="token operator">!</span>childVal<span class="token punctuation">)</span> <span class="token punctuation">{</span> <span class="token keyword">return</span> Object<span class="token punctuation">.</span><span class="token function">create</span><span class="token punctuation">(</span>parentVal <span class="token operator">||</span> <span class="token keyword">null</span><span class="token punctuation">)</span> <span class="token punctuation">}</span>
  <span class="token punctuation">{</span>
    <span class="token function">assertObjectType</span><span class="token punctuation">(</span>key<span class="token punctuation">,</span> childVal<span class="token punctuation">,</span> vm<span class="token punctuation">)</span><span class="token punctuation">;</span>
  <span class="token punctuation">}</span>
  <span class="token keyword">if</span> <span class="token punctuation">(</span><span class="token operator">!</span>parentVal<span class="token punctuation">)</span> <span class="token punctuation">{</span> <span class="token keyword">return</span> childVal <span class="token punctuation">}</span>
  <span class="token keyword">var</span> ret <span class="token operator">=</span> <span class="token punctuation">{</span><span class="token punctuation">}</span><span class="token punctuation">;</span>
  <span class="token function">extend</span><span class="token punctuation">(</span>ret<span class="token punctuation">,</span> parentVal<span class="token punctuation">)</span><span class="token punctuation">;</span>
  <span class="token keyword">for</span> <span class="token punctuation">(</span><span class="token keyword">var</span> key$<span class="token number">1</span> <span class="token keyword">in</span> childVal<span class="token punctuation">)</span> <span class="token punctuation">{</span>
    <span class="token keyword">var</span> parent <span class="token operator">=</span> ret<span class="token punctuation">[</span>key$<span class="token number">1</span><span class="token punctuation">]</span><span class="token punctuation">;</span>
    <span class="token keyword">var</span> child <span class="token operator">=</span> childVal<span class="token punctuation">[</span>key$<span class="token number">1</span><span class="token punctuation">]</span><span class="token punctuation">;</span>
    <span class="token keyword">if</span> <span class="token punctuation">(</span>parent <span class="token operator">&amp;&amp;</span> <span class="token operator">!</span>Array<span class="token punctuation">.</span><span class="token function">isArray</span><span class="token punctuation">(</span>parent<span class="token punctuation">)</span><span class="token punctuation">)</span> <span class="token punctuation">{</span>
      parent <span class="token operator">=</span> <span class="token punctuation">[</span>parent<span class="token punctuation">]</span><span class="token punctuation">;</span>
    <span class="token punctuation">}</span>
    ret<span class="token punctuation">[</span>key$<span class="token number">1</span><span class="token punctuation">]</span> <span class="token operator">=</span> parent
      <span class="token operator">?</span> parent<span class="token punctuation">.</span><span class="token function">concat</span><span class="token punctuation">(</span>child<span class="token punctuation">)</span>
      <span class="token operator">:</span> Array<span class="token punctuation">.</span><span class="token function">isArray</span><span class="token punctuation">(</span>child<span class="token punctuation">)</span> <span class="token operator">?</span> child <span class="token operator">:</span> <span class="token punctuation">[</span>child<span class="token punctuation">]</span><span class="token punctuation">;</span>
  <span class="token punctuation">}</span>
  <span class="token keyword">return</span> ret
<span class="token punctuation">}</span><span class="token punctuation">;</span>
</code></pre></div><p>生命周期钩子和<code>watch</code>被合并为一个数组，然后正序遍历一次执行</p> <h3 id="叠加型"><a href="#叠加型" class="header-anchor">#</a> 叠加型</h3> <p>叠加型合并有：<code>component</code>、<code>directives</code>、<code>filters</code></p> <div class="language-js extra-class"><pre class="language-js"><code>strats<span class="token punctuation">.</span>components<span class="token operator">=</span>
strats<span class="token punctuation">.</span>directives<span class="token operator">=</span>

strats<span class="token punctuation">.</span><span class="token function-variable function">filters</span> <span class="token operator">=</span> <span class="token keyword">function</span> <span class="token function">mergeAssets</span><span class="token punctuation">(</span>
    <span class="token parameter">parentVal<span class="token punctuation">,</span> childVal<span class="token punctuation">,</span> vm<span class="token punctuation">,</span> key</span>
<span class="token punctuation">)</span> <span class="token punctuation">{</span>    
    <span class="token keyword">var</span> res <span class="token operator">=</span> Object<span class="token punctuation">.</span><span class="token function">create</span><span class="token punctuation">(</span>parentVal <span class="token operator">||</span> <span class="token keyword">null</span><span class="token punctuation">)</span><span class="token punctuation">;</span>    
    <span class="token keyword">if</span> <span class="token punctuation">(</span>childVal<span class="token punctuation">)</span> <span class="token punctuation">{</span> 
        <span class="token keyword">for</span> <span class="token punctuation">(</span><span class="token keyword">var</span> key <span class="token keyword">in</span> childVal<span class="token punctuation">)</span> <span class="token punctuation">{</span>
            res<span class="token punctuation">[</span>key<span class="token punctuation">]</span> <span class="token operator">=</span> childVal<span class="token punctuation">[</span>key<span class="token punctuation">]</span><span class="token punctuation">;</span>
        <span class="token punctuation">}</span>   
    <span class="token punctuation">}</span> 
    <span class="token keyword">return</span> res
<span class="token punctuation">}</span>
</code></pre></div><p>叠加型主要是通过原型链进行层层的叠加</p> <h3 id="小结"><a href="#小结" class="header-anchor">#</a> 小结</h3> <ul><li>替换型策略有<code>props</code>、<code>methods</code>、<code>inject</code>、<code>computed</code>，就是将新的同名参数替代旧的参数</li> <li>合并型策略是<code>data</code>, 通过<code>set</code>方法进行合并和重新赋值</li> <li>队列型策略有生命周期函数和<code>watch</code>，原理是将函数存入一个数组，然后正序遍历依次执行</li> <li>叠加型有<code>component</code>、<code>directives</code>、<code>filters</code>，通过原型链进行层层的叠加</li></ul> <h2 id="参考文献"><a href="#参考文献" class="header-anchor">#</a> 参考文献</h2> <ul><li><a href="https://zhuanlan.zhihu.com/p/31018570" target="_blank" rel="noopener noreferrer">https://zhuanlan.zhihu.com/p/31018570<span><svg xmlns="http://www.w3.org/2000/svg" aria-hidden="true" focusable="false" x="0px" y="0px" viewBox="0 0 100 100" width="15" height="15" class="icon outbound"><path fill="currentColor" d="M18.8,85.1h56l0,0c2.2,0,4-1.8,4-4v-32h-8v28h-48v-48h28v-8h-32l0,0c-2.2,0-4,1.8-4,4v56C14.8,83.3,16.6,85.1,18.8,85.1z"></path> <polygon fill="currentColor" points="45.7,48.7 51.3,54.3 77.2,28.5 77.2,37.2 85.2,37.2 85.2,14.9 62.8,14.9 62.8,22.9 71.5,22.9"></polygon></svg> <span class="sr-only">(opens new window)</span></span></a></li> <li><a href="https://juejin.cn/post/6844904015495446536#heading-1" target="_blank" rel="noopener noreferrer">https://juejin.cn/post/6844904015495446536#heading-1<span><svg xmlns="http://www.w3.org/2000/svg" aria-hidden="true" focusable="false" x="0px" y="0px" viewBox="0 0 100 100" width="15" height="15" class="icon outbound"><path fill="currentColor" d="M18.8,85.1h56l0,0c2.2,0,4-1.8,4-4v-32h-8v28h-48v-48h28v-8h-32l0,0c-2.2,0-4,1.8-4,4v56C14.8,83.3,16.6,85.1,18.8,85.1z"></path> <polygon fill="currentColor" points="45.7,48.7 51.3,54.3 77.2,28.5 77.2,37.2 85.2,37.2 85.2,14.9 62.8,14.9 62.8,22.9 71.5,22.9"></polygon></svg> <span class="sr-only">(opens new window)</span></span></a></li> <li><a href="https://juejin.cn/post/6844903846775357453" target="_blank" rel="noopener noreferrer">https://juejin.cn/post/6844903846775357453<span><svg xmlns="http://www.w3.org/2000/svg" aria-hidden="true" focusable="false" x="0px" y="0px" viewBox="0 0 100 100" width="15" height="15" class="icon outbound"><path fill="currentColor" d="M18.8,85.1h56l0,0c2.2,0,4-1.8,4-4v-32h-8v28h-48v-48h28v-8h-32l0,0c-2.2,0-4,1.8-4,4v56C14.8,83.3,16.6,85.1,18.8,85.1z"></path> <polygon fill="currentColor" points="45.7,48.7 51.3,54.3 77.2,28.5 77.2,37.2 85.2,37.2 85.2,14.9 62.8,14.9 62.8,22.9 71.5,22.9"></polygon></svg> <span class="sr-only">(opens new window)</span></span></a></li> <li><a href="https://vue3js.cn/docs/zh" target="_blank" rel="noopener noreferrer">https://vue3js.cn/docs/zh<span><svg xmlns="http://www.w3.org/2000/svg" aria-hidden="true" focusable="false" x="0px" y="0px" viewBox="0 0 100 100" width="15" height="15" class="icon outbound"><path fill="currentColor" d="M18.8,85.1h56l0,0c2.2,0,4-1.8,4-4v-32h-8v28h-48v-48h28v-8h-32l0,0c-2.2,0-4,1.8-4,4v56C14.8,83.3,16.6,85.1,18.8,85.1z"></path> <polygon fill="currentColor" points="45.7,48.7 51.3,54.3 77.2,28.5 77.2,37.2 85.2,37.2 85.2,14.9 62.8,14.9 62.8,22.9 71.5,22.9"></polygon></svg> <span class="sr-only">(opens new window)</span></span></a></li></ul></div> <footer class="page-edit"><!----> <div class="last-updated"><span class="prefix">更新时间:</span> <span class="time">3/2/2022, 7:13:49 PM</span></div></footer> <div class="page-nav"><p class="inner"><span class="prev">
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